Water has become a precious natural resource in the world and approximately 1.2 billion people lack access to safe drinking water. Millions of people die annually—3,900 children a day—from diseases transmitted through unsafe water or human excreta. Sea water accounts for 97.5% of all water on the Earth. So, capturing a small fraction could have a huge impact on water scarcity. However, sea water desalination requires an expensive and energy-intensive process and involves large-scale facilities. Pre-existing desalination technologies are based on membrane separation via reverse osmosis (RO) and thermal distillation, with RO accounting for over 50% of the installed capacity. Conventional thermal desalination processes are inefficient in their use of energy and suffer particularly from corrosion, as well as scaling that also affects RO. Recent research on the transport of water through hydrophobic double-walled carbon nanotubes is promising, demonstrating water fluxes that are over three orders of magnitude higher than those predicted from continuum hydrodynamic models (Holt et al., Science, 2006, 312 (5776), pp. 1034-1037). However, integrating carbon nanotubes into the membrane remains challenging.
A recently developed desalination method based on ion concentration polarization (ICP) offers an interesting alternative to the membrane-based approach to desalination. This approach minimizes membrane fouling by using an energy barrier as a salt ion filter and can be more energy-efficient than the traditional RO. Kim et al. (Nature Nanotechnology 5, 297-301, 2010) have demonstrated this technology inside a microfluidic chip. However, this microfluidic approach does not have a sufficient throughput (˜10 μL/min) and has not been scaled up. For this reason, a large-scale device based on ICP has not previously been demonstrated.